Cluster chemistry: XXXIX. Gold—ruthenium clusters with sulphur ligands: Synthesis and structure of HRu3Au(μ3-S)(CO)9(PPh3), Ru3Au(μ3-SBut)(CO)9(PPh3) and Ru3Au2(μ3-S)(CO)9(PPh3)2

H₂Ru₃(μ₃-S)(CO)₉ is deprotonated by K[HBBu^s₃] to give cluster anions which react with [O{Au(PPh₃)}₃]⁺ or with AuCl(PPh₃)/T1⁺ to give HRu₃Au(μ₃-S)(CO)₉(PPh₃) (1) and Ru₃Au₂(μ₃-S)(CO)₉(PPh₃)₂ (3). A similar sequence with HRu₃(μ₃-SBu^t)(CO)₉ leads to Ru₃Au(μ₃-SBu^t)(CO)₉(PPh₃) (2) as the main product although some 1 also forms, indicating SC cleavage competes with deprotonation of HRu₃(μ₃-SBu^t)(CO)₉ by [HBBu^s₃]^?. The X-ray crystal structures of 1, 2 and 3 are described; (1) and (2) have “butterfly” AuRu₃ cores with markedly different hinge angles of 119 and 148° respectively, while 3 has a trigonal-bipyramidal Au₂Ru₃ skeleton. All three clusters have the sulphur atom symmetrically bridging the Ru₃ triangular face.     

Cluster chemistry: XXXIII. Reactions of [{Au(PPh3)}3O]+ with [Ru3(μ3-C2But)(CO)9]−: X-ray structure of [Ru3Au2(μ3-CCHBut)(CO)9(PPh3)2], containing a t-butylvinylidene ligand attached to a trigonal-bipyramidal Ru3Au2 core

Deprotonation (K[HBBu₃^s]) of HRu₃(μ₃-C₂Bu^t)(CO)₉, followed by reaction of the anion with [O{Au(PPh₃)}₃][BF₄], afforded the known complex Ru₃Au(μ₃-C₂Bu^t)(CO)₉ (9%), the vinylidene cluster Ru₃Au₂(μ₃-CCHBu^t)(CO)₉(PPh₃)₂ (16%) and the hexanuclear Ru₃Au₃(C₂Bu^t)(CO)₈(PPh₃)₃ (3%). The X-ray structure of the pentanuclear complex shows an asymmetric trigonal-bipyramidal Ru₃Au₂ core (Ru, Au at the apices) with the Ru₃ face bridged by a t-butylvinylidene ligand, being σ-bonded to Ru(1) and Ru(3), and η²-coordinated to Ru(2). Crystals are monoclinic, space group P2₁/n with a 19.121(3), b 13.109(3), c 23.649(4) Å, β 106.76(2)° and Z = 4. The structure was solved using 4405 observed diffractometer data, and refined to R 0.044, R_w 0.047.     

Cluster chemistry: XXX. Reaction of a triruthenium anion with [O{Au(PPh3)}3][BF4]: Synthesis and structure of Ru3Au3(μ3-2η1,η3-C12H15)(CO)8(PPh3)3

The cluster HRu₃(μ₃-C₁₂H₁₅)(CO)₉ is rapidly deprotonated by K[HBBu₃^sec] in tetrahydrofuran, generating the anion [Ru₃(μ₃-C₁₂H₁₅)(CO)₉]^? in high yield. Reaction between this anion and [O{Au(PPh₃)}₃][BF₄] gives Ru₃Au₃(μ₃-C₁₂H₁₅)(CO)₈(PPh₃)₃ (2) as the main product, shown by an X-ray study to contain a capped trigonal-bipyramidal Ru₃Au₃ core in which the C₁₂H₁₅ ligand is bonded in the μ₃-2η¹,η³ fashion to the Ru₃ face. An alternative formulation involving the cyclo-Au₃(PPh₃)₃ moiety acting as a three-electron donor to the Ru₃ cluster is discussed. Crystals of 2 are monoclinic, space group P2₁/c, a 13.574(1), b 40.634(4), c 14.617(2) Å, β 92.58(1)°, Z = 4; 3233 data with I > 3σ(I) were refined to R = 0.078, R_w = 0.084.     

Cluster Chemistry: XXVIII. Utility of fast atom bombardment mass spectrometry for the characterisation of high molecular weight complexes containing metal clusters

Fast atom bombardment (FAB) mass spectrometry has been used to obtain spectra of HRu₃Au(μ₃-S)(CO)₉(PPh₃), Ru₃Au₂(μ₃-S)(CO)₉(PPh₃)₂ and Ru₃Au₃(μ₃-C₁₂H₁₅)(CO)₈(PPh₃)₃, none of which give metal-containing ions in conventional EI mass spectrometry. All the compounds give molecular (M⁺) or quasimolecular ([M + 2H]⁺) ions which fragment by conventional routes.     

The reaction of Ru3(CO)12 with HC9PPh2)3. Characterisation of Ru3(CO)9[HC(PPh2)3], and crystal and molecular structure of Ru3(CO)9[HC(PPh2)(PhPC6H4PPh)]·CHCl3

Reaction of Ru₃(CO)₁₂ with HC(PPh₂)₃ leads to a variety of products, two of which have been characterised. One is the symmetrically capped product Ru₃(CO)₉[HC(PPh₂)₃], which was characterised spectroscopically. The second product was characterised crystallographically as Ru₃(CO)₉[HC(PPh₂)-(PhPC₆H₄PPh)]-CHCl₃.     

Synthesis and structural characterisation of [Au2Pt2(PPh3)4(CN-xylyl)4](PF6)2: A platinum—gold cluster with a flattened butterfly geometry

[Au₂Pt₂(PPh₃)₄(CN-xylyl)₄](PF₆)₂ (CN-xylyl = 2,6-dimethylphenylisocyanide) has been synthesised from [Pt(C₂H₄)(PPh₃)₂] and [Au(CN-xylyl)₂]⁺ in CH₂Cl₂ and in the presence of an excess of CN-xylyl. A single crystal X-ray diffraction study has demonstrated that the metal atoms define a flattened butterfly with the gold atoms occupying the higher connectivity sites and forming a short bond of length 2.590(2) Å. The platinum—gold distances lie in the range 2.710(2)–3.026(2) Å.     

Dreizentren-oxidative Addition von Phosphor-Yliden an Ru3(CO)12

Three-Centre Oxidative Addition of Phosphorus Ylides to Ru₃(CO)₁₂ Phosphorus ylides undergo oxidative addition to Ru₃(CO)₁₂ to yield a wide range of Ru₃ clusters with triply bridging organic ligands derived from the ylides. Ph₃PCH₂ forms HRu₃(CO)₉(μ₃1-Ph₃P — CH — CO) ( 1 ) containing a phosphonio enolate. Ph₃PCH — CHO yields a product mixture containing the phosphonio enolate-bridged cluster and its PPh₃ derivative 6 , the phosphoniomethylidyne-bridged compound H₂Ru₃(CO)₉(μ₃1-C — PPh₃) ( 5 ), and the ketenylidene-bridged compound H₂Ru₃(CO)₈(PPh₃)(μ₃1-C — CO) ( 7 ). Thermal treatment converts the phosphonio enolate ligand (in 1 ) into the phosphoniomethylidyne ligand (in 5 ), and the latter into the ketenylidene ligand (in 7 ). With Ph₃PCH — C(O)Me and Ru₃(CO)₁₂ ortho1-metalated Ru₃ derivatives 10, 11 of the phosphonio ketone R₃P — C — C(O)Me are produced, and likewise with Ph₃PCH — COOEt the ortho1-metalated derivative 12 of the phosphonio ester R₃P — C — CO₂Et. Me₃PCH — COOtBu is oxidatively added to form HRu₃(CO)₉(μ₃1-Me₃P — C — COOtBu) ( 13 ) bearing a phosphonio ester ligand. — The crystal structures of 6 and 13 are reported. The sequence of Ru₃ clusters and the bonding modes of the μ₃ ligands can be related to the surface reactions during Fischer-Tropsch catalysis.     

[cis‐{η2‐(Ph3PAu)2}Ph3PCr(CO)4]·THF,featuring the shortest known separation between two Au metal centres in a heteronuclear Au2M cluster

The title compound, tetra­carbonyl‐1κ⁴C‐tris­(tri­phenyl­phos­phino)‐1κP,2κP,3κP‐triangulo‐chromiumdigold(Au—Au)(2 Cr—Au) tetra­hydro­furan solvate, [Au₂Cr(C₁₈H₁₅P)₃(CO)₄]·C₄H₈O, is a stable isolobal analogue of the extremely labile [(η²‐H₂)CrL_n–1] molecular hydrogen complex (n = 6; L is a neutral ligand, e.g. CO or PPh₃), and features the shortest known separation [2.6937 (2) Å] between two Au atoms in a triangular heteronuclear metal‐cluster framework.     

Synthesis and molecular structure of [Au3Ru4(μ3-H)(CO)12(PPh3)3]

The title compound can be prepared in good yield by heating either [Ru₄(μ-H)₄(CO)₁₂] or [Au₂Ru₄(μ₃-H)₂(CO)₁₂(PPh₃)₂] with [AuMe(PPh₃)] in toluene. The related compound [Au₃Ru₄(μ₃-H)(μ-dppm)(CO)₁₂(PPh₃)] has also been prepared. Both trigoldtetraruthenium clusters undergo dynamic behaviour in solution, involving intramolecular rearrangement of the metal core, as revealed by variable temperature NMR studies. The crystal structure of [Au₃Ru₄(μ₃-H)(CO)₁₂(PPh₃)₃] has been established by an X-ray diffraction study. The metal atom core comprises a trigonal bipyramidal AuRu₄ unit with two AuRu₂ faces capped by gold atoms.     

Synthesis and characterisation of HRuRh3(CO)12. Crystal structures of HRuRh3(CO)12, HRuRh3(CO)10(PPh3)2 and HRuCo3(CO)10(PPh3)2

A new ruthenium-rhodium mixed-metal cluster HRuRh₃(CO)₁₂ and its derivatives HRuRh₃(CO)₁₀(PPh₃)₂ and HRuCo₃(CO)₁₀(PPh₃)₂ have been synthesized and characterized. The following crystal and molecular structures are reported: HRuRh₃(CO)₁₂: monoclinic, space group P2₁/c, a 9.230(4), b 11.790(5), c 17.124(9) Å, β 91.29(4)°, Z = 4; HRuRh₃(CO)₁₀(PPh₃)₂·C₆H₁₄: triclinic, space group P$\text{1}$, a 11.777(2), b 14.079(2), c 17.010(2) Å, α 86.99(1), β 76.91(1), γ 72.49(1)°, Z = 2; HRuCo₃(CO)₁₀(PPh₃)₂·CH₂Cl₂: triclinic, space group P$\text{1}$, a 11.577(7), b 13.729(7), c 16.777(10) Å, α 81.39(4), β 77.84(5), γ 65.56°, Z = 2. The reaction between Rh(CO)₄^? and (Ru(CO)₃Cl₂)₂ tetrahydrofuran followed by acid treatment yields HRuRh₃(CO)₁₂ in high yield. Its structural analysis was complicated by a 80–20% packing disorder. More detailed structural data were obtained from the fully ordered structure of HRuRh₃(CO)₁₀(PPh₃)₂, which is closely related to HRuCo₃(CO)₁₀(PPh₃)₂ and HFeCo₃(CO)₁₀(PPh₃)₂. The phosphines are axially coordinated.     

Preparation and Characterization of an Unusual Di-Cobalt Complex; X-Ray Crystal Structure of Co(CO)2(μ-CO)(μ:η2,η4-C4Ph4)Co(CO)2(PPh3)

Reaction of [MoCo(CO)₅(PPh₃)₂(η⁵-C₅H₅)] (1) with diphenylacetylene in tetrahydrofuran at 50 °C yielded two heterobimetallic compounds, [MoCo(CO)₄.(PPh₃){μ-PhC ? CPh}(η⁵-C₅H₅)] (4) and [MoCo(CO)₅{μ-PhC ? CPh} (η⁵-C₅H₅)] (5). However, an unexpected product, Co(CO)₂(μ-CO)(μ:η₂,η⁴-C₄Ph₄)Co(CO)₂(PPh₃) (6), was observed while attempting to grow the crystals for structural determination of 4. The X-ray crystal structure of 6 was determined: triclinic, $ {\rm P}\bar 1 $, a = 11.654(2) Å, b = 12.864(2) Å, c = 13.854(2) Å, α = 89.67(2)°, β = 86.00(2)°, γ= 83.33(2)°, V = 2057.9(6) ų Z=2. In 6, two cobalt fragments are at apical and basal positions of the pseudo-pentagonal pyramidal structure, respectively. The electron count for the apical cobalt fragments is 20, which is rather unusual. It is believed that 6 was formed after the fragmentation and recombination of the fragmented species of 4.     

The reaction of Ru3(CO)12 and Os3(CO)12 with PH2Ph; the x-ray crystal structures of HRu3(CO)10(PHPh) and H2Ru3(CO)9(PPh)

Twelve new trinuclear complexes containing terminal PH₂Ph, edge-bridging PHPh and/or capping PPh ligands have been isolated from the reaction of M₃(CO)₁₂ (M = Ru or Os) with PH₂Ph in refluxing solvents. HRu₃(CO)₁₀(PHPh) (IIIa) crystallises in the monoclinic space group P2₁/c with a = 8.761(3), b = 11.402(4), c = 22.041(7) Å,β = 98.89(2)°, and Z = 4. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.027 for 3676 unique observed intensities. The X-ray analysis shows that one edge of the Ru₃ triangle is bridged by a hydride and the PHPh ligand, and that the phosphorus-bound hydrogen atom lies over the metal triangle and the phenyl group away from it. This provides an explanation for the ready formation of the capped species H₂Ru₃(CO)₉(PPh) (Va) on pyrolysis of the edge-bridged complex as opposed to the previously reported conversion of HOs₃(CO)₁₀(NHPh) to an orthometallated derivative under similar conditions. An X-ray analysis of H₂Ru₃(CO)₉-(PPh) (Va) confirms the capped geometry. the complex crystallises in the monoclinic space group P2₁/n with a = 9.323(4), b = 15.110(6), c = 45.267(15) Å,β = 91.84(3)°, and Z = 12. the structure was solved and refined using the same techniques as described previously. The final residual R is 0.061 for 4839 reflections. Some reactions of Va show that the phosphorous cap is difficult to displace and stabilises the molecule with respect to decomposition to non-cluster species.     

[Au(C6F5)3(PPh2H)]: A Precursor for the Synthesis of Gold(III) Phosphide Complexes

The covalent radius of Au ^I is about 0.07 Å smaller than that of Ag^I. This was determined from the crystal structures of the isostructural complexes [N(PPh₃)][{Au(C₆F₅)₃(μ-PPh₂)}₂M] (M=Au (structure shown in the picture), Ag). These mixed Au^III–M phosphides were synthesized from [Au(C₆F₅)₃(PPh₂H)], the first gold complex to contain a secondary phosphane.     

Low oxidation state ruthenium chemistry : IV. The reactions of M(CO)2(PPh3)3 complexes (M = Fe,Ru) and the hydrogenation and isomerization of alkenes catalyzed by RuL(CO)2(PPh3)2 (L = H2, PPh3)

The complexes M(CO)₂(PPh₃)₃ (I, M = Fe; II, M = Ru) readily react with H₂ at room temperature and atmospheric pressure to give cis-M(H)₂(CO)₂(PPh₃)₂ (III, M = Fe;IV,M = Ru). I reacts with O₂ to give an unstable compound in solution, in a type of reaction known to occur with II which leads to cis-Ru(O₂)(CO)₂(PPh₃)₂(V). Even compound IV reacts with O₂ to give V with displacement of H₂; this reaction has been shown to be reversible and this is the first case where the displacement of H₂ by O₂ and that of O₂ by H₂ at a metal center has been observed. III and IV are reduced to M(CO)₃(PPh₃)₂ by CO with displacement of H₂; Ru(CO)₃- (PPh₃)₂ is also formed by treatment of IV with CO₂, but under higher pressure. Compounds II and IV react with CH₂CHCN to give Ru(CH₂CHCN)(CO)₂- (PPh₃)₂(VI) which reacts with H₂ to reform the hydride IV.cis-Ru(H)₂(CO)₂(PPh₃)₂(IV) has been studied as catalyst in the hydrogenation and isomerization of a series of monoenes and dienes. The catalysts are poisoned by the presence of free triphenylphosphine. On the other hand the ready exchange of H₂ and O₂ on the “Ru(CO)₂(PPh₃)₂” moiety makes IV a catalyst not irreversibly poisoned by the presence of air. It has been found that even Ru(CO)₂(PPh₃)₃(II) acts as a catalyst for the isomerization of hex-1-ene at room temperature under an inert atmosphere.     

Bis­[bis­(di­phenyl­phosphino­methyl)­phenyl­phosphine]­di­chloro­tetra­gold(I) bis­[chloro­tris­(penta­fluoro­phenyl)­aurate(III)]

The cation of the title compound, [Au₄(PPh₂CH₂PPhCH₂PPh₂)₂Cl₂][Au(C₆F₅)₃Cl]₂ or [Au₄Cl₂(C₃₂H₂₉P₃)₂][AuCl(C₆F₅)₃]₂, displays a rhomboidal geometry for the Au atoms, with short Au?Au distances of 3.104 (2) and 3.185 (1) Å; the linear coordination at the Au^I atoms is distorted: P—Au—P 164.7 (2)° and P—Au—Cl 170.67 (11)°. The anion shows the expected square‐planar geometry at Au^III, with the Au atom 0.022 (5) Å out of the plane of the four donor atoms.     

Photochemical reactions of (CO)2 (PPh3)MnC5H4Fe(CO)2C5H5 and (CO)2(PPh3)MnC5H4COFe(CO)2C5H5 with PPh3

Conclusions The photochemical reactions of (CO)₂(PPh₃)MnC₅H₄Fe(CO)₂C₅H₅ and (CO)₂(PPh₃)MnC₅H₄COFe(CO)₂C₅H₅ with PPh₃ gave the products of replacing the CO on the Fe atom by PPh₃: respectively (CO)₂(PPh₃)MnC₅H₄Fe (CO)(PPh₃)C₅H₅ and (CO)₂(PPh₃)MnC₅H₄COFe(CO)(PPh₃)C₅H₅.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2813–2815, December, 1977.     

Aktivierung von Schwefelkohlenstoff an Trirutheniumclustern: Synthese und Kristallstruktur von [Ru3(CO)5(μ‐H)2(μ‐PCy2)(μ‐Ph2PCH2PPh2){μ‐η2‐PCy2C(S)}(μ3‐S)] und [Ru3(CO)5(CS)(μ‐H)(μ‐PtBu2)(μ‐PCy2)2(μ3‐S)]

Activation of Carbon Disulfide on Triruthenium Clusters: Synthesis and X‐Ray Crystal Structure Analysis of [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐Ph₂PCH₂PPh₂){μ‐η²‐PCy₂C(S)}(μ₃‐S)] and [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] [Ru₃(CO)₆(μ‐H)₂(μ‐PCy₂)₂(μ‐dppm)] ( 1 ) (dppm = Ph₂PCH₂PPh₂) reacts under mild conditions with CS₂ and yields by oxidative decarbonylation and insertion of CS into one phosphido bridge the opened 50 VE‐cluster [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐dppm){μ‐η²‐PCy₂C(S)}(μ₃‐S)] ( 2 ) with only two M–M bonds. The compound 2 crystallizes in the triclinic space group P 1 with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; α = 84.65(3), β = 77.21(3), γ = 81.87(3)° and V = 2790.7(11) ų. The reaction of [Ru₃(CO)₇(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂] ( 3 ) with CS₂ in refluxing toluene affords the 50 VE‐cluster [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] ( 4 ). The compound cristallizes in the monoclinic space group P 2₁/a with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; β = 104.223(16)° and V = 4570.9(10) ų. Although in the solid state structure one elongated Ru–Ru bond has been found the complex 4 can be considered by means of the ³¹P‐NMR data as an electron‐rich metal cluster.     

Cluster chemistry: XXXVIII. Reactions between M(C2R)(PR′3 (M = Cu,Ag, Au; R = Ph,C6F5; R′ = Me Ph) and H2Os3(CO)10: X-ray structures of Os3Au(μ-CHCHR)(CO)10(PPh3) (R = Ph and C6F5)

The reactions of Os₃(μ-H)₂(CO)₁₀ with a series of Group IB metal acetylide-tertiary phosphine complexes are described. Whereas the compounds M(C₂C₆F₅)(PPh₃) (M = Cu, Ag, Au) afforded the complexes MOs₃(μ-CHCHC₆F₅)(CO)₁₀(PPh₃) cleanly and in high yield, complex mixtures of products were obtained from reactions of the analogous phenylacetylides. The complexes MOs₃(μ-CHCHPh)(CO)₁₀(PPh₃), MOs₃(μ-CHCHPh)(CO)₉(PPh₃)₂ and MOs₃(μ-H)(CO)₁₀(PPh₃) (of known structure), and MOs₃(μ-CHCHPh)(CO)₉(PPh₃)₂ and HMOs₃(CHCPh)(CO)₈ (of unknown structure) were characterised; Au(C₂Ph)(PMe₃) afforded similar derivatives. The reactions proceed by oxidative-addition and hydrogen migration steps; MP bond cleavage reactions also occur to a small extent. The molecular structures of AuOs₃(μ-CHCHC₆R₅)(CO)₁₀(PPh₃) (R = F or H) were determined by X-ray analyses. For R = F, crystals are triclinic, space group P$\text{1}$ with a 9.081(2), b 13.291(2), c 17.419(2) Å, α 84.49(1), β 76.20(2), γ 75.81(2)° and Z = 2; 4622 observed data [I > 2.5σ(I)] were refined to R = 0.027, R_W = 0.031. For R = H, crystals are triclinic, space group P$\text{1}$, with a 9.403(4), b 13.448(3), c 13.774(4) Å, α 83.34(2), β 88.66(3), γ 70.21(3)°, and Z = 2; 4405 observed data [I > 2.5σ(I)] were refined to R = 0.030, R_W = 0.033. The two molecules differ in the orientation of the Ph rings of the PPh₃ groups, but are otherwise similar to Os₃(μ-H)(μ-CHCHBu^t)(CO)₁₀ with the μ-H ligand replaced by the isolobal μ-Au(PPh₃) group.     

THE CRYSTAL AND MOLECULAR STRUCTURE OF Ru3(CO)9(PPh3)3

Abstract

The synthesis of tertiary phosphine and phosphite substituted derivatives of M₃(CO)₁₂ {M = Ru(1a) Os(1b)} is discussed and the X-ray crystal and molecular structure of the tris-triphenylphosphine substituted ruthenium cluster Ru₃(CO)₉(PPh₃)₃ (2a) is reported. Complex 2a crystallises in the monoclinic space group P2₁/n with cell parameters a = 14.180(9), b = 21.644(14), c = 18.248(10) Å, β = 92.52(5)°, V = 5595(6) Å ³, Z = 4. The structure was solved by full-matrix least-squares methods based on F ². The refinement converged at R1 = 0.0564, wR2 = 0.2125 for 4857 observed data [F > 4σ(F)].     

Bonding and Acidity of the Formal Hydride in the Prototypical Au9(PPh3)8H2+ Nanocluster

The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au₉(PPh₃)₈H²⁺ nanocluster, formed by addition of a hydride to the well-characterized Au₉(PPh₃)₈³⁺. Using gas-phase infrared spectroscopy, we were able to unambiguously isolate Au₉(PPh₃)₈H²⁺ and Au₉(PPh₃)₈D²⁺, revealing an Au−H stretching mode at 1528 cm⁻¹ that shifts to 1038 cm⁻¹ upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster-H bonding that has some square-well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm⁻¹ in the Au−H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au₉(PPh₃)₈H²⁺, at least with regard to its surface reactivity.